1. Field of the Invention
The present invention relates to a hydrodynamic bearing having a composite capillary seal section for preventing lubricating fluid retained in the hydrodynamic bearing from leaking to the outside of the bearing by utilizing both the capillary force and rotational centrifugal force.
2. Background Art
In a hard disk drive device or removable disk drive device, a hydrodynamic bearing has conventionally been used as a bearing of a motor for driving a recording disk, that generates dynamic pressure by lubricating fluid (for example, oil) retained in a bearing gap between a shaft and a sleeve when the motor rotates. Various types of a hydrodynamic bearing have been proposed.
This hydrodynamic bearing is required to reduce as much as possible the leakage of the oil, retained in the bearing gap, to the outside to thereby ensure the lifetime of the oil and to maintain the characteristic of the hydrodynamic bearing in a stable manner over a long period. In the hydrodynamic bearing using oil as working fluid as described above, a tapered seal gap (hereinafter referred to as a capillary seal section) is formed at the edge section of the hydrodynamic bearing, wherein oil is retained in the capillary seal section while forming a vapor-liquid surface between the oil and air in the capillary seal section.
In the capillary seal section in the hydrodynamic bearing, the size of the gap in the radial direction formed in the capillary seal section is gradually expanded as the capillary seal section is away from the hydrodynamic bearing, whereby a difference occurs in the capillary force of the oil depending upon the position where the vapor-liquid face of the oil retained in the gap in the radial direction is formed. Therefore, the capillary seal section has a function of supplying oil therefrom, in case where the amount of oil retained in the hydrodynamic bearing decreases, and a function of accommodating the increasing amount in case where the volume of the oil retained in the hydrodynamic bearing increases due to the temperature rise of the oil or the like.
A composite capillary seal section has recently been proposed, as a motor having a rotor that rotates at extremely high speed, that utilizes “capillary force” of the oil and “rotational centrifugal force acted when the motor rotates” to thereby firmly prevent the oil from flowing to the outside of the hydrodynamic bearing.
The composite capillary seal section of this type is formed in a gap in the radial direction between an inclined face 1a of a rotor 1 and an inclined face 2a of a stationary member 2, as shown in FIG. 13. The size of the gap in the radial direction between the inclined faces 1a and 2a of the rotor 1 and the stationary member 2 is gradually expanded toward an opening side (the downward side in the figure) of the composite capillary seal section 3, whereby oil 4 is retained in the composite capillary seal section 3. Further, a center axis line M of the radial-direction gap in the composite capillary seal section 3 is inclined toward the direction in which it gradually approaches the rotation axis line X, whereby upon the rotation of the rotor 1, the composite capillary seal section 3 pumps the oil 4 toward the hydrodynamic bearing (the upward side in the figure) by the rotational centrifugal force.
In the hydrodynamic bearing having the composite capillary seal section 3, the more the inclination angle of the central axis line M of the radial-direction gap in the composite capillary seal section 3 increases with respect to the rotation axis X, the more the rotational centrifugal force that pumps the oil 4 toward the hydrodynamic bearing can be increased upon the rotation of the rotor 1. Moreover, in the hydrodynamic bearing provided with the composite capillary seal section 3, the sealing function can be enhanced as the size of the radial-direction gap in the capillary seal section 3 is reduced as much as possible and the vapor-liquid face of the oil 4 is positioned in more proximate to the hydrodynamic bearing.
In this case, however, the vapor-liquid face 4a of the oil 4 retained in the composite capillary seal section 3 is shifted toward the hydrodynamic bearing, so that it is difficult to observe the vapor-liquid face 4a, i.e., the management of the filling amount of the oil 4 since the inclined face 1a of the rotor 1 interferes. As a result, in case where the filling amount of the oil 4 in the hydrodynamic bearing is small, the oil 4 may be exhausted, or in case where the filling amount is too much, the oil 4 may flow to the outside of the composite capillary seal section 3, thereby being difficult to ensure the lifetime of the hydrodynamic bearing and arising a fear of deteriorating reliability of the hydrodynamic bearing.